Porous acrylic fiber and fabric comprising the same, and method of producing the same

ABSTRACT

Porous acrylic fibers produced by a method comprising subjecting a spinning dope containing 0.3 to 20 parts by weight of poly(vinyl acetate) relative to 100 parts of an acrylic copolymer to a wet spinning to give fibers, crimping and cutting the fibers, subjecting the resultant fibers to a treatment by hot water at 90 to 100° C. for 30 to 120 minutes or by saturated steam at 90 to 130° C. for 10 to 90 minutes to thereby form porous fibers; and a pile fabric having pile portions which comprise the porous fibers in an amount of 3 wt % or more, and, in the pile fabric, respective single fibers are visible being separate and emphasized, and thus the pile fabric has an appearance being highly decorative and excellent in design characteristics.

RELATED APPLICATIONS

This application is a nationalization of PCT application PCT/JP00/07063filed Oct. 12, 2000. This application claims priority from the PCTapplication and Japan Application Serial No. H11(1999)-290771 filed Oct.13, 1999; Japan Application Serial No. H11(1999)-290772 filed Oct. 13,1999; Japan Application Serial No. H11(2000)-281128 filed Sep. 18, 2000.

TECHNICAL FIELD

The present invention relates to an acrylic fiber used mainly in pilefabrics, a pile fabric comprising this acrylic fiber, and a method ofproducing this acrylic fiber, and more particularly relates to anacrylic fiber which is easily porosified by a porosification treatmentoperation following spinning, and which has an external appearance inwhich a feeling of the presence of individual fibers is emphasized, anda pile fabric which is manufactured using this fiber, and which hasextremely superior external appearance characteristics in which afeeling of the presence of individual fibers constructing the pile partis visually emphasized.

BACKGROUD ART

Acrylic type synthetic fibers have a fur-like hand and luster, and arewidely used in the knit field, as well as in the boa and high-pilefields. In recent years, furthermore, there has been an increased demandto make the external appearance and hand of piles resemble those ofnatural fur more closely by using such acrylic fibers. In natural furs,the standing-hair portion of the fur generally has an intrinsictwo-layer structure consisting of long hairs known as “guard hairs”, andshort hairs known as “down hairs” which grow densely beneath the guardhairs. Pile fabrics are fabrics which mimic this natural fur structure“as is”; acrylic type synthetic fibers have already seen wide use inpile products as a result of the natural hand and luster of such fibers.Usually, acrylic fibers used in the field of such pile products aresubjected to working such as the creation of a shading effect bykneading a metallic compound into the fibers in order to cause theluster to resemble that of natural fur. For example, in Japanese PatentApplication Laid-Open No.S56-44163, Japanese Patent ApplicationLaid-Open No.S56-44164 and the like, methods are proposed in whichacrylic fibers that have a fur-like luster are obtained by addingmetallic compounds and cellulose derivatives to copolymers consisting ofacrylonitrile. Furthermore, in Japanese Patent Application Laid-OpenNo.H3-146705, it is indicated that a fur-like luster can be realized bysubjecting acrylic type synthetic fibers following drying (in which ametallic compound is added during the spinning process) to rapid coolingand overdrawing so that the fibers have cracks that are perpendicular tothe axial direction of the fibers. However, although fibers obtained bythese techniques have a fur-like external appearance at first glance,the impression that the individual fibers are covered by othersurrounding fibers cannot be eliminated in cases where individual fibersare formed into a standing-hair fabric. Furthermore, in Japanese PatentApplication Laid-Open No.H9-31797, it is indicated that in a pile fabricobtained by constructing the fabric from fibers produced by adding adelustering agent at the rate of 1.5 wt % or less to dischargeablefibers having a fixed thickness, and fibers containing such adelustering agent at the rate of 0.7 wt % or less, fibers with differentbrightness values are present in aggregations, so that the fabric has awood-like coloring showing a grain. However, most of these effectsrelate to the print coloring characteristics in the pile fabric, and arenot effects in which a feeling of the presence of individual fibers isvisually emphasized in cases where the fabric is formed into astanding-hair fabric.

Thus, in the past, there have been few reports of fibers showing anexternal appearance in which a feeling of the presence of the individualfibers is emphasized in a pile fabric. Such reports include a techniquein which the vaporization of a low-boiling-point solvent is utilized toendow the fiber cross section with voids (as indicated in JapanesePatent Application Laid-Open No.S62-177255) as a technique relating tocoloring properties utilizing the porous structure of fibers. However,since this technique uses a low-boiling-point solvent as a bubblingagent, the technique suffers from a problem in terms of manufacture:namely, it is difficult to recover the low-boiling-point solvent used toform voids in the fiber cross section.

Meanwhile, in regard to fibers in which acrylic type copolymers arecombined with other polymers, a fiber obtained by utilizing a voidstabilizing agent such as cellulose acetate to stabilize the voids inthe manufacturing process of the fiber is introduced in (for example)Japanese Patent Application Laid-Open No.S54-101920, and a fiberobtained by mixing cellulose acetate with an acrylic polymer produced bycopolymerizing monomers containing 3 wt % or more sulfonate groups isintroduced in Japanese Patent Application Laid-Open No.H6-2213. However,both of these fibers aim at improving the hygroscopic properties, sothat the application of the fibers differs from that of the presentinvention. Moreover, these fibers are used in fields that require awater-absorbing/perspiration-absorbing function, such as underwear,socks, sportswear, towels and the like; accordingly, the denier of thefibers is small, and it appears from the embodiments that the width inthe direction of the major axis of the fiber cross section, i. e., themaximum width, is 60 μm or less. Furthermore, an acrylic fiber which hasa rubber-form polymer such as a polyvinyl acetate in an acryliccopolymer is introduced in Japanese Patent Application Laid-OpenNo.S60-110913; however, this fiber aims at preventing fiber splitting,and does not aim at endowing a fabric with an external appearance thatis superior in design quality, in which a feeling of the presence ofindividual fibers (of the type described above) is emphasized.Furthermore, this fiber does not have a porous structure. Moreover, inregard to fibers in which a modacrylic type polymer and a vinyl acetatetype polymer are combined, a porous fiber obtained by utilizingphase-separated polymers such as a modacrylic type polymer and a vinylacetate type polymer, and arranging the process so that a void structureformed in the spinning process is maintained after spinning, isintroduced in Japanese Patent Application Laid-Open No.S57-58811;however, the object in this case is to improve the hygroscopicity bymeans of voids formed by phase separation. Furthermore, the addition ofa vinyl acetate type polymer to an acrylonitrile type polymer isdisclosed in Japanese Patent Application Laid-Open No.H10-110326;however, this technique relates to process stability with the aim ofincreasing the productivity of acrylic fibers, and does not aim atemphasizing a feeling of the presence of the fibers, i. e., at obtainingan external appearance in which the individual fibers are visuallyemphasized, as in the present invention.

Thus, in the past, there has been no technique of obtaining an externalappearance in which the individual fibers are emphasized byporosification following spinning.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide a pilefabric which is endowed with external appearance characteristics thatare superior in terms of design quality, i. e., in which a feeling ofthe presence of the individual fibers forming the pile part isemphasized, by porosifying acrylic fibers and using these porous acrylicfibers to form the pile fabric. More specifically, it is an object ofthe present invention to provide a novel porous acrylic fiber which cangive an external appearance that is superior in terms of design quality,in which a feeling of the presence of the individual fibers is visuallyemphasized in the standing-hair part of a pile fabric, and in which sucha special feature of the external appearance can be caused to appearconspicuously by porosification of the fiber in after-working followingspinning, and a method of producing this fiber.

As a result of diligent research conducted by the present inventors inorder to achieve the abovementioned object, it appeared that it wasnecessary to form a structure in which visible light passing through theinteriors of the fibers is to some extent scattered and reflected inorder to obtain an external appearance in which a feeling of thepresence of the individual fibers is emphasized in the fibers of thestanding-hair portion of a pile fabric. Accordingly, the inventorsfurther investigated a method in which components with differentrefractive indices are caused to be present in blocks, and the materialforming the fibers is porosified; in addition, the inventorsinvestigated the thickness that allows the fibers of the standing-hairportion to be visually recognized as individual fibers. Specifically,considering novel fibers which can be porosified by an after-process andwhich have an external appearance in which a feeling of the presence ofthe fibers is emphasized, the inventors focused on the cohesive forceand incompatibility of the internal constituent components of the fibersin order to form fibers in which a porosified structure can easily berealized by the action of heat and water that can generally be used inan after-process even in the case of fibers that have a homogeneousstructure on the macroscopic level, and investigated polymers that havea strong phase separation effect and that show good fiber moldabilityeven when mixed. As a result, the inventors discovered a method wherebyporosification can be accomplished utilizing the effects of heat andmoisture of after-working by specifying the types of polymers added evenin the case of fibers in which the voids have already been baked out byheating effected by drying, heat treatment or the like, although therelationship between the porous structure of the gel-form fibersobtained by the wet spinning of acrylic type copolymers and there-porosified fiber structure obtained by after-working is unclear. Thisdiscovery led to the perfection of the present invention.

Specifically, the porous acrylic fiber of the present invention is aporous acrylic fiber which consists chiefly of a resin compositioncontaining 0.3 to 20 parts by weight of polyvinyl acetate per 100 partsby weight of acrylic type copolymer, and in which the rate of the dropin the specific gravity as calculated by the following Equation (1) isin the range of 5.0 to 20%.

Rate of drop in specific gravity (%)=100×(1−Da/Db)  (Equation 1)

[In the above equation, Da indicates the specific gravity value of theporous acrylic fiber, and Db indicates the true specific gravity valueresin consisting of the acrylic type copolymer.]

It is desirable that the abovementioned acrylic type copolymer be acopolymer consisting essentially of 35 to 98 wt % acrylonitrile and 2 to65 wt % other monomer that is copolymerizable with acrylonitrile.Furthermore, it is even more desirable that the abovementioned acrylictype copolymer be a copolymer consisting essentially of 35 to 98 wt %acrylonitrile, 2 to 65 wt % vinyl chloride and/or vinylidene chloride,and 0 to 10 wt % sulfonate-group-containing monomer that iscopolymerizable with these compounds.

Furthermore, in regard to the resin composition of the abovementionedporous acrylic fiber, this composition may contain 0.3 to 20 parts byweight polyvinyl acetate and 0.5 to 15 parts by weight cellulose resinper 100 parts by weight of acrylic type copolymer. Cellulose acetate,cellulose propionate and cellulose acetate butyrate are desirable as theabovementioned cellulose resin.

In the abovementioned acrylic fiber, it is desirable that the major-axiswidth in the fiber cross section be 70 to 300 μm.

The method of the present invention for producing such a porous acrylicfiber is a method which is characterized in that a fiber formed bywet-spinning a spinning stock solution containing 0.3 to 20 parts byweight of polyvinyl acetate per 100 parts by weight of acrylic typecopolymer, or a fiber formed by wet-spinning a spinning stock solutioncontaining 0.3 to 20 parts by weight of polyvinyl acetate and 0.5 to 15parts by weight cellulose resin per 100 parts by weight of acrylic typecopolymer, is subjected to crimping and cutting treatments, and is thenporosified by a hydrothermal treatment for 30 to 120 minutes at 90 to100° C. and/or a saturated steam treatment for 10 to 90 minutes at 90 to130° C. The abovementioned hydrothermal treatment may also be a dyeingoperation.

The porous acrylic fiber of the present invention is a porous acrylicfiber that is manufactured by the abovementioned production method, andis preferably a fiber in which the rate of the drop in the specificgravity calculated by the following Equation (2) from the specificgravity (Dp) prior to porosification and the specific gravity (Da) ofthe porosified fiber is in the range of 3.0 to 15%.

 Rate of drop in specific gravity (%)=100×(1−Da/Dp)  (Equation 2)

The pile fabric of the present invention consists of the abovementionedporous polyacrylic fiber. In this pile fabric, it is desirable that theabovementioned porous acrylic fiber be contained in the pile part at therate of 3 wt % or greater. Furthermore, it is desirable that this pilefabric be a pile fabric having a step difference that has at least along-pile part and a short-pile part, and that the abovementioned porousacrylic fiber be contained in the long-pile part. Moreover, it isdesirable that this pile fabric contain the abovementioned acrylic fiberat the rate of 5 to 60 wt % in the pile part as a whole. In theabovementioned pile fabric having a step difference, it is desirablethat the difference between the mean pile length of the long-pile partand the mean pile length of the short-pile part be 2 mm or greater, andthat the mean pile length of the long-pile part be 12 to 70 mm.

The present invention will be described in greater detail below.

The acrylic type copolymer that forms the acrylic fiber of the presentinvention contains acrylonitrile as the chief component of thecopolymer, and is a copolymer with a vinyl type monomer that iscopolymerizable with this acrylonitrile. The abovementioned acrylic typecopolymer is preferably a copolymer that contains 35 to 98 wt %acrylonltrile and other vinyl type monomers that are copolymerizablewith acrylonitrile. Even more preferably, the acrylonitrile content is35 to 90 wt %. Examples of the abovementioned vinyl type monomers thatare copolymerizable with acrylonitrile include vinyl halide andvinylidene halides as represented by vinyl chloride, vinylidenechloride, vinyl bromide, vinylidene bromide and the like, unsaturatedcarboxylic acids as represented by acrylic acid and methacrylic acid,and salts of these acids, acrylic acid esters and methacrylic acidesters as represented by methyl acrylate and methyl methacrylate, vinylesters as represented by vinyl acetate and vinyl butyrate, vinyl typeamides as represented by acrylamide and methacrylamide,sulfonate-group-containing monomers as represented by methallylsulfonicacid, styrenesulfonic acid and salts of these acids, and other compoundssuch as vinylpyridine. methylvinyl ether, methacrylonitrile and thelike. The acrylic type copolymer may be an acrylic type copolymerobtained by copolymerizing one or more of these compounds. Moreover,styrenesulfonic acid, para-styrenesulfonic acid, allylsulfonic acid,methallylsulfonic acid, para-methacryloyloxybenzenesulfonic acid,methacryloyloxypropylsulfonic acid and metal salts or amine salts ofthese acids may be used as the abovementioned sulfonate-group-containingvinyl type monomers. In the present invention, a copolymer consistingessentially of 35 to 98 wt % acrylonitrile, 2 to 65 wt % vinyl chlorideand/or vinylidene chloride and 0 to 10 wt % sulfonate-group-containingvinyl type monomer that is copolymerizable with these compounds isdesirable. Of course, the present invention is not adversely affectedeven if the acrylic type copolymer constituting the main component thatforms the acrylic fiber consists of a polymer with a differentcomposition and copolymerization proportions. Examples of solvents thatcan be used for the wet spinning of such copolymers include organicsolvents such as acetone, acetonitrile, dimethylformamide,dimethylacetamide, dimethyl sulfoxide and the like.

The polyvinyl acetate (hereafter abbreviated to “PVAc”) used may be acommercially marketed PVAc, and may be dissolved beforehand in thesolvent used in the spinning stock solution of the acrylic typecopolymer, or may be directly dissolved in the spinning stock solution.Alternatively, this PVAc may be solution-polymerized by a universallyknown technique using the solvent that forms the spinning stock solutionof the acrylic type copolymer, and this polymer solution may be used. Ifnecessary, the PVAc may be partially or completely saponified, and thetype of solvent used in the spinning stock solution may be appropriatelyselected in accordance with the solubility. For example, in cases wheredimethyl sulfoxide is used as the solvent, use is possible even at adegree of saponification of 99.5% or greater; on the other hand, incases where acetone is used as the solvent, the degree of saponificationis 50% or less, preferably 40% or less. The reason for this is that incases where the degree of saponification is 50% or greater, thesolubility of PVAc in acetone drops, so that the filterability of thespinning stock solution drops, thus having a deleterious effect on thespinnability. The amount of PVAc that is added to the acrylic typecopolymer is preferably in the range of 0.3 to 20 parts by weight per100 parts by weight of the acrylic type copolymer, and is even morepreferably in the range of 1 to 10 parts by weight per 100 parts byweight of the acrylic type copolymer. If the amount added is less than0.3 parts by weight, the porosifying effect of the hydrothermaltreatment and/or saturated steam treatment performed following spinningis insufficient, so that porosified fibers with the desired externalappearance cannot be obtained. Specifically, an increase in thebrightness, which is one of the three elements of the color that appearswhen the fibers are colored to a desired hue, cannot be obtained, sothat an external appearance in which a feeling of the presence of theindividual fibers is emphasized cannot be achieved. On the other hand,if the amount of PVAc that is added exceeds 20 parts by weight, thestate of phase separation between the acrylic type copolymer and thePVAc is increased, so that the spinning stability and coagulation in thefiber forming process deteriorate, thus making continuous productiondifficult. Accordingly, such a large amount is undesirable.

In regard to the cellulose resin, cellulose acetate, cellulosepropionate or cellulose acetate butyrate may be used; as in the case ofthe PVAc, the resin used may be appropriately selected In accordancewith the type and solubility of the solvent used in the spinning stocksolution. In cases where acetone is used as a solvent, it is desirablethat the degree of acetification of cellulose acetate be 52 to 59%. Theamount added is preferably 0.5 to 15 parts by weight per 100 parts byweight of the acrylic type copolymer, and is even more preferably 1 to10 parts by weight per 100 parts by weight of the acrylic typecopolymer. If the amount added is less than 0.5 parts by weight, thephase separation effect caused by the cellulose resin drops.Furthermore, there is an accompanying drop in the synergistic effectcaused by the addition of PVAc, so that the desired external appearancecannot be obtained. On the other hand, if the amount added exceeds 15parts by weight, the spinning stability and drawability in the fiberforming process deteriorate, so that there is a drop in the continuousproductivity or productivity per unit time. Accordingly, such a largeamount is undesirable.

In regard to the adding and mixing of the PVAc and cellulose resin withthe acrylic type copolymer, these ingredients can be directly mixed andagitated inside the spinning stock solution tank, with defoaming thenbeing performed to form the spinning stock solution. Alternatively, aline mixer such as a dope grinder, static mixer or the like can be usedin the process that immediately precedes the spinning nozzle in thespinning stock solution feeding line.

Various types of additives such as stabilizers and anti-oxidants for thepurpose of preventing decomposition or coloring caused by heat andlight, modifiers for the purpose of improving dyeing characteristics,anti-static agents, hygroscopicity-improving agents, coloring agentssuch as pigments, dyes and the like for coloring the fibers to thedesired hue, various types of delustering agents, and polymers for thepurpose of improving other fibers characteristics, may be added to thespinning stock solution for the purpose of improving the fiberperformance, with these additives being varied according to variousrequired fiber characteristics, and added in amounts that do notinterfere with the object of the present invention. In particular, ifadditives that have the effect of making the fibers opaque are used incombination with the above components, the minor-axis width of the fibercross section can be reduced with respect to the object of the presentinvention.

The polymer concentration of the spinning stock solution used in thepresent invention is generally adjusted to a value of 20 to 35 wt %, andis preferably adjusted to a value of 25 to 32 wt % if spinnability andprocess stability are taken into account. In cases where thisconcentration is less than 20 wt %, the amount of solvent extractionagent that is discharged from the nozzle is increased, so that itbecomes difficult to obtain a uniform cross section. On the other hand,if the concentration exceeds 35 wt %, the viscosity increases so thatthe spinning stock solution tends to gel, and so that monofilamentbreakage during spinning becomes common.

The spinning stock solution prepared by mixing specified polymers asdescribed above can be formed into a fiber by a universally knownspinning method for acrylic fibers. It is desirable that the denier ofthe acrylic fiber in this case be 2 to 50 decitex (hereafter abbreviatedto “dtex”). In particular, a denier in the range of 3 to 30 dtex makesit easier to obtain the abovementioned special features, and istherefore ideal. If the denier is less than 2 dtex, the fibers becometoo slender so that a feeling of the presence of individual short fiberscannot be obtained when the fibers are formed into a pile fabric. On theother hand, if the denier exceeds 50 dtex, the fibers become too thick,so that the resulting pile fabric tends to have a hard hand;accordingly, such a large denier is undesirable. Furthermore, there areno particular restrictions on the fiber cross section; however, a flat,elliptical, crescent-shaped or dog-bone-shaped cross section isdesirable. In this case, in order to emphasize the visual effect, thewidth of the fiber cross section in the direction of the major axis, i.e., the maximum width, is preferably 70 μm or greater, more preferably90 μm or greater, and even more preferably 110 μm or greater. The upperlimit on this width is 300 μm. In cases where the maximum width exceedsthis limit, the impression of a fiber-form film which imparts adisharmonious sensation in which planarity is emphasized to a fargreater extent than the linear images of the individual fibers becomesstrong, which is undesirable. If the maximum width is less than thelower width of 70 μm, there is a lack of any feeling of the presence ofindividual fibers. Furthermore, this width of the fiber cross section inthe direction of the major axis (maximum width) refers to the maximumdistance between two parallel lines circumscribing the fiber crosssection. Meanwhile, in a case where the width of the fiber cross sectioncontained by two lines parallel to the direction of width in thedirection of the major axis, i. e., parallel to the direction of themaximum width, is taken as the minor axis, the width in the direction ofthis minor axis is preferably 8 μm or greater, and is even morepreferably 10 μm or greater. In cases where this width is less than 8μm, a transparent image is emphasized when the fibers are viewed from adirection perpendicular to the direction of the major axis of the fibercross section, so that a feeling of the presence of individual fibers islacking. Here, the term “flattened} does not necessarily indicate astrict rectangular shape; as long as the flattening ratio (ratio of themajor-axis width to the minor-axis width) is 2.5 or greater in a casewhere the maximum width of the fiber cross section is taken as the majoraxis, and the width of the fiber cross section contained by two linesparallel to the major axis is dad taken as the minor axis, thecross-sectional shape is not particularly restricted, and may beelliptical or crescent-shape, and may also include indentations andprojections as in a group of spikes or pot lid. On the other hand, ifthe flattening rate exceeds 25, a transparent image is emphasized whenthe fibers are viewed from a direction perpendicular to the major-axisdirection, and the fiber cross section tends to split: accordingly, sucha flattening rate is undesirable.

Necessary treatments and operations such as the application of an oilingagent, mechanical crimping, cutting and the like are performed on thefiber obtained as described above. In this case, the term “mechanicalcrimping” refers to crimping obtained by a universally known method suchas a gear crimping process, stuffing box process or the like. There areno particular restrictions on this crimping; however, a desirablecrimped shape is a shape with a crimping degree of 4 to 15%, preferably5 to 10%, and with 6 to 15 peaks/inch, preferably 8 to 13 peaks/inch, asthe number of crimping peaks. The abovementioned crimping degree isobtained by a measurement method of the type represented by the methoddescribed in JIS-L1074. Afterward, these fibers are cut. There are noparticular restrictions on the fiber length of the cut fibers; however,in the case of use in a pile fabric, it is desirable to cut the fibersto an appropriately selected length in the range of 20 to 180 mm.

When the fibers are subjected to a hydrothermal treatment and/orsaturated steam treatment after being subjected to crimping and cuttingtreatments as described above, with these fibers preferably beingexposed to a moist atmosphere at a temperature of approximately 100° C.to 120° C., voids are generated in the interior portions of the fibersso that the fibers become porous. The term “porous” as used in theporous acrylic fiber of the present invention preferably refers to aconfiguration in which (for example) numerous voids with a diameter ofseveral tens of nanometers extending In the direction of length of thefibers are present as shown in FIG. 1. The hydrothermal treatment and/orsaturated steam treatment that are used in order to porosify the acrylicfiber as described above differ from the universally known pressurizedsteam treatment performed for the purpose of heat treatment relaxationin the manufacturing process of acrylic fibers in that such ahydrothermal treatment and/or saturated steam treatment are performedfor the purpose of fiber porosification. These treatments are performedon fibers that have at least been dried and subjected to treatments suchas drawing or the like, and are performed on the fibers in anafter-treatment process following crimping and cutting treatments. Thereason that the fibers are porosified by this hydrothermal treatmentand/or saturated steam treatment is apparently that the dense structureformed by the drawing, drying, heat treatment or steam relaxationtreatment in the fiber manufacturing process is converted into a stablestructure as a result of the plasticization of the acrylic typecopolymer caused by the effects of excess moisture such as wet steam,hot water or the like in the hydrothermal treatment of saturated steamtreatment, with voids being generated at the boundary surfaces with thePVAc and cellulose resin, which have poor compatibility with the acrylictype copolymer. Furthermore, the reasons for the synergistic effect ofPVAc and the cellulose resin are unclear; however, it appears thatincreased density or the generation of voids is at first prevented inthe fiber manufacturing process by the adhesion and hydrophilicizingeffect of PVAc, and that phase separation of the three componentsforming the fibers is further promoted by the effect of drawing moistureinto the interior portions of the fibers in the subsequent moistatmosphere.

In regard to the treatment conditions of the abovementioned hydrothermaltreatment, the treatment temperature is 90 to 100° C., preferably 95 to100° C. In cases where the treatment temperature is lower than 90° C., asufficient drop in the specific gravity of the fiber is not observedregardless of the treatment time, so that the porosification of thefiber is insufficient. The treatment time of the hydrothermal treatmentin this case is 30 to 120 minutes, preferably 60 to 90 minutes. Thereasons for this are as follows: specifically, in cases where thetreatment time is less than 30 minutes, a sufficient drop in thespecific gravity of the fiber does not occur, so that the desiredporosified fiber cannot be obtained. On the other hand, in cases wherethe treatment time exceeds 120 minutes, yellowing of the fibers occurs.Furthermore, in regard to the treatment conditions of the saturate steamtreatment, the treatment temperature is 90 to 130° C., preferably 98 to110° C. The reasons for this are as follows: specifically, in caseswhere the treatment temperature is lower than 90° C., no drop in thespecific gravity of the fiber is observed regardless of the treatmenttime, so that the porosification of the fiber is insufficient, as in thecase of the hydrothermal treatment. On the other hand, in cases wherethe treatment temperature exceeds 130° C., the problem of yellowing ofthe fibers occurs. The steam treatment time in this case is 5 to 90minutes, preferably 10 to 60 minutes. The reasons for this are asfollows: specifically, in cases where the treatment time is less than 5minutes, a sufficient drop in the specific gravity of the fiber does notoccur, so that the desired porosified fiber cannot be obtained. On theother hand, in cases where the treatment time exceeds 90 minutes,yellowing of the fibers occurs.

The term “hydrothermal treatment” as used in the present inventionrefers to a treatment in which the fibers are immersed in hot water at aspecified temperature, as performed using a universally known Obermeyermachine. In the p resent invention, the desired porosification isaccomplished even if a dyeing operation is performed as this treatment;accordingly, the present invention also has the merit of not requiringthe provision of an additional process for the purpose ofporosification. The porous fibers that are colored to a desired hue bysuch a combination porosification treatment and dyeing operationgenerally have a high brightness (L value) caused by coloring comparedto colored fibers that do not possess porosity, and show a special typeof color. This visual special feature becomes conspicuous when themaximum width of the fiber cross section exceeds 70 μm as describedabove, so that the object of the present invention is sufficientlyachieved.

Furthermore, as a concrete example of the saturated steam treatmentperformed in the present invention, the fibers are packed into astainless steel basket, and this basket is set in a pressurize steamer,so that the fibers are treated at a specified temperature.

The degree of porosification of the abovementloned acrylic fibers can beadjusted to some extent by adjusting the respective contents of the PVAcand cellulose resin present in the fibers, and by adjusting thetemperature and time of the porosification treatment. Furthermore, inorder to make the visual effect obtained by porosification moreconspicuous, it is desirable to set the rate of the drop in the specificgravity of the porous acrylic fiber with respect to the true specificgravity of the resin consisting of the acrylic type copolymer in therange of 5.0% to 20% and more preferably in the range of 7.0% to 15%,and to set the rate of the drop in the specific gravity before and afterthe hydrothermal treatment or saturated steam treatment as describedabove, in the range of 3.0% to 15%, and more preferably in the range of3.0% to 10%. Specifically, the degree of porosification can bedetermined not only from the external appearance, but also from thechange in the specific gravity of the fibers. Furthermore, the rate ofthe drop in the specific gravity value (Da) of the porous acrylic fiberof the present invention relative to the true specific gravity value(Db) of the resin consisting of the acrylic type copolymer is in therange of 3.0% to 15%, and is preferably in the range of 3.0% to 10%. Byforming a pile fabric using fibers that have thus been porosified, it ispossible to manufacture a pile fabric that has an external appearancewith superior design quality, in which a feeling of the presence of theindividual fibers that form the pile fabric is emphasized. In caseswhere the rate of the drop of the specific gravity (Da) of the porousacrylic fiber from the true specific gravity (Db) based in the acrylictype copolymer is less, than 5.0%, or the rate of the abovementioneddrop in the specific gravity before and after porosification is lessthan 3.0%, the fibers are insufficient as porous fibers, so that afeeling of the presence of individual short fibers is not visuallyemphasized in the pile fabric, and special external appearancecharacteristics cannot be obtained. On the other hand, in cases wherethe rate of the drop in the specific gravity (da) of the porous acrylicfiber with respect to the true specific gravity (Db) based on theacrylic type copolymer exceeds 20%, or in cases where the rate of thedrop in the specific gravity before and after porosification exceeds15%, there is a deleterious effect on the mechanical properties of thefibers.

Here, the abovementioned “true specific gravity value (Db) of the resinconsisting of the acrylic type copolymer” is the specific gravitydetermined by the substitution-in-water method for the acrylic typecopolymer resin compression-molded using a tablet agent molding deviceor the like prior to the dissolution of the resin in the solvent. Therate of the drop in the specific gravity of the porous acrylic fiberrelative to the true specific gravity value (db) of the resin consistingof the acrylic type copolymer is calculated using the following Equation(1) from the specific gravity value (Da) of the porous acrylic fiber andthe abovementioned true specific gravity value (Db) of the resinconsisting of the acrylic type copolymer.

Rate of drop in specific gravity (%)=100×(1−Da/Db)  (Equation 1)

Furthermore, the abovementioned rate of the drop in the specific gravitybefore and after porosification is calculated using the followingEquation (2) from the specific gravity (Dp) of the fiber prior toporosification and the specific gravity (Da) of the fiber porosified bythe hydrothermal treatment and/or saturated steam treatment.Furthermore, the abovementioned specific gravity of the fiber ismeasured according to the substitution-in-water method of JIS K7112.

Rate of drop in specific gravity (%)=100×(1−Da/Db)  (Equation 2)

Furthermore, the pile fabric of the present invention is manufacturedusing the porous acrylic fiber obtained as described above, and is apile fabric in which the abovementioned porous acrylic fiber iscontained in the pile part at the rate of 3 wt % or greater, preferably10 to 70 wt %. In cases where the proportion of the porous acrylic fiberin the pile part is less than 3 wt %, the color difference from otherfibers is insufficient, so that superior external appearancecharacteristics in which a feeling of the presence of individual fibersis emphasized cannot be obtained.

The term “pile part” used in the present invention refers to thestanding-hair part of the pile fabric (standing-hair fabric) excludingthe portion that consists of the base fabric (base yarn portion).Furthermore, the term “pile lengths” refers to the length from the rootsof the abovementioned standing-hair part to the tip ends of thestanding-hair part. Furthermore, the term “mean pile lengths” refers tothe mean value obtained when the length from the roots of the fibersforming the pile part (i. e., the roots of the pile fabric surface) tothe long pile parts is measured in ten places with the fibers formingthe pile part in the pile fabric caused to stand up in a verticalattitude so that the fibers are lined up in a uniform manner.

In general, pile fabrics consist of various types of fabrics, includingfabrics with a fixed pile length and fabrics in which long and shortpile parts are mixed. In the pile fabric of the present invention, thereare no particular restrictions on the abovementioned pile length;however, it is more effective if the pile fabric is a pile fabric thathas a step, i. e., a two-stage pile with a long pile part and a shortpile part, or a three-stage pile with a long pile part, an intermediatepile part and a short pile part. For example, in a three-stage pile ofthe type shown in FIG. 2, the abovementioned “long pile part” refers tothe so-called guard hair part in which the pile length is the longest(part a), the “intermediate pile part” refers to the so-called middlehair part in which the pile length is next longest (part b) after thatof the long pile part, and the “short pile part” refers to the so-calleddown hair in which the pile length is shortest (part c). The “stepdifference” in the present invention is expressed as the differencebetween part a and part c in the case of a two-stage pile, and as thedifference between part a and part b in the case of a pile with three ormore stages. Furthermore, such a step difference can be created usingshrunken fibers or fibers that have different cut lengths.

Another preferable construction of the pile fabric of the presentinvention is a pile fabric which has a step difference of theabovementloned type, and which contains porous acrylic fibers as thefibers that form the long pile part in the pile fabric, with the contentof such porous acrylic fibers among the fibers that form the pile partbeing 5 to 60 wt %, and preferably 10 to 50 wt %. In cases where porousacrylic fibers are used only in the intermediate pile part and shortpile part, the porous acrylic fibers of the present invention which havesuperior external appearance characteristics are covered by the otherfibers used as guard hairs, so that superior external appearancecharacteristics tend not be obtained when the fibers are formed into apile fabric. Furthermore, in cases where the proportion of porousacrylic fibers used as the fibers that form this long pile part is lessthan 5 wt % of the overall pile part, and large numbers of other fibersare used as guard hairs, the porous acrylic fibers are covered by theseother fibers, so that a sufficient effect in terms of externalappearance characteristics cannot be obtained. On the other hand, incases where this proportion exceeds 60 wt %, the proportion of porousacrylic fibers in the pile fabric becomes excessively large, so thatguard hairs predominate; as a result, the step effect tends to beinsufficiently expressed.

The method of development used to obtain a pile fabric consisting ofacrylic fibers with superior external appearance characteristics can beappropriately set according to commercial designs for pile fabrics;however, if the abovementioned acrylic fibers with a large flatteningrate and thick denier are used in a pile fabric, a finish that isvisually emphasized to a much greater extent can be obtained. In thecase of a method of use in which the proportion of the abovementionedacrylic fibers in the guard hair part is small, these acrylic fibersstand out in a sparse manner, which is effective as a so-called visualeffect, and the non-bundling of the fibers is further emphasized so thatthe fabric shows a more fur-like hand with a superior hair-looseningeffect.

Furthermore, in regard to the respective proportions of the long pilepart and short pile part in the overall pile, it is desirable to use aconstruction in which the ratio of the long pile part/short pilepart=10˜85 wt %/15˜90 wt %. The step difference between the pile lengthof the fibers occupying the long pile part and the pile length of thefibers occupying the short pile part is 2 mm or greater, and ispreferably 3 mm or greater. Furthermore, the pile length of the fibersoccupying the long pile part is 12 to 70 mm, and is preferably 15 to 50mm. In cases where the step difference is less than 2 mm, the boundarybetween the guard hairs and the down hairs tends to become indistinct;as a result, the effect of the present invention, which is made moredistinct by such a step difference, becomes insufficient. Furthermore,in cases where the pile length of the long pile part is less than 12 mm,the abovementioned step effect cannot be sufficiently observed even ifthere is a significant step difference in the pile part. As a result, aconspicuous effect is not obtained. Conversely, if the pile length ofthe long pile part exceeds 70 mm, the abovementioned acrylic fibers inthe pile fabric lack a feeling of body, so that the fabric is inadequateas a standing-hair product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a model cross-sectional view of a porous acrylic fiber;

FIG. 1(B) is a model longitudinal-sectional view of the same; and

FIG. 2 is a model diagram of a pile fabric showing the step differencein a three-stage pile.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be concretely described below in terms ofexamples; however, the present invention is not limited in any way bythese examples.

Prior to the description of examples, the analysis and measurementconditions and evaluation methods used will be described.

(A) Denier

The denier was measured using an auto-vibro type denier measuring device“Denier Computer DC-11” (manufactured by Search Seigyo Denki); the meanvalue for a sample number n=25 was used.

(B) Fiber Cross-Sectional Length and Flattening Ratio

The fiber cross section on which Au had been vacuum-evaporated by meansof an Ion Coater IB-3 (manufactured by Eiko Engineering) was observedusing an S-3500N scanning electron microscope (manufactured by HitachiSeisakusho) (scanning electron microscopic observation; hereafterreferred to as “SEM observations”), and the major-axis width andminor-axis width were measured. Mean values for n=25 were used for the mmajor-axis width and minor-axis width. The flattening ratio (=major-axiswidth/minor-axis width) was determined from these major-axis width andminor-axis width values.

(C) Specific Gravity of Fibers

The specific gravity of the fibers was determined using an automaticspecific gravity meter (high-precision model) D-H100 (manufactured byToyo Seiki Seisakusho) in accordance with the substitution-in-watermethod of JIS K7112, with approximately 150 g of unraveled fabric beingtaken as a sample. Furthermore, the water used in the measurement of thespecific gravity was prepared by adding a fluorine type surfactant todistilled water at the rate of 0.8 g/L. When the sample was immersed,the immersion rate was set at a rate slower that the rate of wettingcaused by the capillary effect of the sample, and care was taken toinsure that no bubbles were present between the fibers.

(D) Rate of Drop in Specific Gravity from True Specific Gravity of FiberConsisting of Acrylic Type Copolymer

Samples formed by compressing the acrylic type copolymer resin intosolid tablets using a tablet molding device (pressure: 18 to 20 ton/cm²)were measured in the same manner as described in (C) above in accordancewith JIS K7112, thus determining the true specific gravity value (Db) ofthe resin consisting of the abovementioned acrylic type copolymer.Furthermore, in cases where the true specific gravity value of the resinconsisting of the acrylic type copolymer is determined from the porousacrylic fibers, this can be measured by preparing samples in which thefinely cut fibers (preferably cut fibers that will pass through a 200mesh sieve) are molded into a solid tablet using a tablet molding devicein the same manner as described above. However, if large amounts ofadditives other than the acrylic type copolymer are present, a slighterror will be generated; accordingly, it is desirable to measure thisvalue using only the acrylic type copolymer resin. In cases whereadditives are present, the true specific gravity value (Db) of theacrylic type copolymer can also be calculated with the theoreticalspecific gravity values of the additives being taken into account. Forexample, in a case where 0.3 to 20 parts by weight of PVAc is added to100 parts by weight of the acrylic type copolymer, a converted valueobtained by multiplying the specific gravity value determined from thefibers using the abovementioned method by 0.99 to 0.985 may be taken asthe true specific gravity value of the acrylic type copolymer.

The rate of the drop in the specific gravity was calculated using thefollowing Equation (1) from the true specific gravity value (Db) of theresin consisting of the abovementioned acrylic type copolymer determinedas described above, and the specific gravity value (Da) of the porousacrylic fibers.

Rate of drop in specific gravity (%)=100×(1−Da/Db)  (Equation 1)

(E) Rate of Drop in Specific Gravity Before and After Porosification

This rate of drop was calculated using the following Equation (2) fromthe specific gravity (Dp) prior to porosification and the specificgravity (Da) of the fibers porosified by the hydrothermal treatmentand/or saturated steam treatment.

Rate of drop in specific gravity (%)=100×(1−Da/Db)  (Equation 2)

F) Brightness: L Value

Fibers which had been unraveled and weighed out to a fixed weight wereplaced in a sample holder with a diameter of 30 mm, and the brightnesswas measured using a Type Σ 90 color difference meter (manufactured byNippon Denshoku Kogyo) equipped with a light source conforming to thestandard light source C described in JIS Z 8710. At the time ofmeasurement, the dyed fabric sample was adjusted to a fabric sampledensity of 0.16 g/cm³ and placed in the sample cell, and the L value wasmeasured.

(G) Evaluation of External Appearance of Porous Acrylic Fibers

Fabric samples that were crimped, thoroughly unraveled and laminatedwere separated by approximately 50 cm, and the center portions of thelaminated fabric samples were visually observed by 10 judges, and thefeeling of a presence of individual short fibers was judged according towhether or not the single overlapping fibers could be individuallydistinguished. The judgement criteria were set as the following fourgrades:

⊚: Individual fibers can be distinguished very easily even in an overallobservation, so that the feeling of the presence of such fibers isstrong.

◯: Individual fibers can be distinguished easily even in an overallobservation, so that a feeling of the presence of such fibers isrecognized.

Δ: It is somewhat difficult to distinguish individual fibers in anoverall observation, so that a feeling of the presence of such fibers isnot recognized to any great extent.

X: Individual fibers can be distinguished by carefully directed visualobservation, so that a feeling of the presence of such fibers can berecognized to a limited extent: in an overall observation, however, itis difficult to distinguish the individual fibers, so that a feeling ofthe presence of such fibers cannot be recognized.

(H) Evaluation of External Appearance Characteristics of Pile Fabric

(i) Preparation of Pile Fabric

Using the acrylic fibers obtained by the present invention, a pilefabric was knitted by means of a sliver knitting machine. Next, apre-polishing treatment and a pre-shearing treatment were performed at120° C. so that the pile length was made uniform. Afterward, the backsurface of the pile was back-coated with an acrylic ester type adhesiveagent. Subsequently, polishing was performed at 155° C., followed bybrushing; then, polishing and shearing were performed in combination(two processes each) at 135° C., 120° C. and 90° C., and the crimp ofthe standing-hair surface layer was removed, thus producing astanding-hair fabric with a fixed pile length.

(ii) Evaluation of External Appearance

For the pile fabrics prepared by the method described in (i) above, thedegree of external appearance characteristics in which a feeling of thepresence of the individual short fibers forming the pile part wasemphasized was evaluated by a sensual evaluation from the standpoints ofvisual and sensual perception using three evaluation grades, with thisevaluation being performed according to the following criteria:

◯: The product has external appearance characteristics in which afeeling of the presence of the individual short fibers in the pilefabric is emphasized to a considerable extent.

Δ: The abovementioned feeling of the presence of the individual shortfibers in the pile fabric is inferior.

X: The abovementioned feeling of the presence of the individual shortfibers in the pile fabric is markedly inferior.

(I) Mean Pile Length

The length from the roots of the fibers forming the pile part (the rootsof the pile fabric surface) to end of the long pile part was measured inten places using slide calipers after the fibers forming the pile partin the pile fabric were caused to stand in a vertical attitude so thatthe fibers were lined up in a uniform manner, and the mean values of themeasurements thus obtained was taken as the mean pile length.

(J) Pile Step Difference

The “pile step difference” refers to the difference between the meanpile length of the long pile part and the mean pile length of the shortpile part measured by the abovementioned method: this pile stepdifference was a calculated using the following equation:

Step difference (mm)=mean pile length (mm) of long pile part−mean pilelength (mm) of short pile part.

EXAMPLES 1 and 2

A acrylic type copolymer consisting of 49 wt % acrylonitrile, 50 wt %vinyl chloride and 1 wt % sodium styrenesulfonate was dissolved inacetone, and 5 parts by weight of PVAc was further added per 100 partsby weight of the abovementioned acrylic type copolymer, thus producing asolution with a polymer concentration of 29 wt %. This solution was usedas a spinning stock solution, and was wet-spun via a spinning nozzlewith 3900 holes having a hole size of 0.08×0.6 mm into a solidifyingbath consisting of an aqueous solution with a 30% concentration ofacetone. Next, the spun fibers were passed through two baths consistingof aqueous solutions with respective acetone concentrations of 55% and25%, and were drawn to a draw ratio of 2.0 times. Afterward, primarydrawing was performed to a draw ratio of 3.0 times (in combination withthe abovementioned drawing) in a water rinse bath at 75° C. Then, afteran oiling agent was applied to the fibers thus obtained, the fibers weredried in an atmosphere at 110° C., and were further drawn at 125° C. sothat the final draft was 6.5 times. Next, the fibers were heated in adry-heat atmosphere at 145° C., thus producing fibers with a denier of16.5 dtex. Next, appropriate oiling agent application and mechanicalcrimping were performed on these fibers using universally known methods,and the fibers were further cut to 51 mm. Afterward, the fibers werepacked into an Obermeyer dyeing machine at a packing density of 0.30g/cm³, and were subjected to a hydrothermal treatment for 60 minutes at98° C. (Example 1); alternatively, the fibers were packed into astainless steel basket, and this basket was placed in a pressurizedsteamer, where a saturated steam treatment was performed for 20 minutesat 105° C. (Example 2). In this way, the desired fibers were produced.

EXAMPLE 3

An acrylic type copolymer consisting of 52 wt % acrylonitrile, 47 wt %vinylidene chloride and 1 wt % sodium styrenesulfonate and 10 parts byweight of PVAc was further added per 100 parts by weight of theabovementioned acrylic type copolymer, thus producing a solution with apolymer concentration of 29 wt %. This solution was used as a spinningstock solution, and was wet-spun via a spinning nozzle with 3900 holeshaving a hole size of 0.08×0.6 mm into a solidifying bath consisting ofan aqueous solution with a 25% concentration of acetone. Next, the spunfibers were passed through two baths consisting of aqueous solutionswith respective acetone concentrations of 30% and 15%, and were drawn toa draw ratio of 2.0 times. Afterward, primary drawing was performed to adraw ratio of 3.0 times (in combination with the abovementioned drawing)in a water rinse bath at 85° C. Then, after an oiling agent was appliedto the fibers thus obtained, the fibers were dried in an atmosphere at110° C., and were further drawn at 125° C. so that the final draft was6.5 times. Next, the fibers were heated in a dry-heat atmosphere at 145°C., thus producing fibers with a denier of 16.5 dtex. Next, appropriateoiling agent application and mechanical crimping were performed on thesefibers using universally known methods, and the fibers were further cutto 51 mm. Afterward, the fibers were packed into an Obermeyer dyeingmachine at a packing density of 0.30 g/cm³, and were subjected to ahydrothermal treatment for 60 minutes at 98° C., thus producing thedesired fibers.

EXAMPLES 4 and 5

An acrylic type copolymer consisting of 93 wt % acrylonitrile and 7 wt %vinyl acetate was dissolved in dimethylacetamide (hereafter abbreviatedto “DMAc”), and a spinning stock solution with a polymer concentrationof 25 wt % was obtained by further adding 1 part by weight of PVAc to100 parts by weight of the abovementioned acrylic type copolymer. Thisspinning stock solution was wet-spun via a spinning nozzle with 3900holes having a hole size of 0.08×0.6 mm into a solidifying bathconsisting of an aqueous solution with a 60% concentration of DMAc, andwas further drawn to a draw ratio of 5.0 times while the solvent waswashed away in boiling water. Next, an oiling agent was applied, and thefibers were dried by means of hot rollers at 150° C. Afterward, thefibers were subjected to a relaxation treatment in pressurized steam ata gauge pressure of 0.25 MPa, thus producing fibers with a denier of16.5 dtex. Next, appropriate oiling agent application and mechanicalcrimping were performed on these fibers using universally known methods,and the fibers were further cut to 51 mm. Afterward, the fibers werepacked into an Obermeyer dyeing machine at a packing density of 0.30g/cm³, and were subjected to a hydrothermal treatment for 60 minutes at98° C. (Example 4); alternatively, the fibers were packed into astainless steel basket, and this basket was placed in a pressurizedsteamer, where a saturated steam treatment was performed for 30 minutesat 105° C. (Example 5). In this way, the desired fibers were produced.

COMPARATIVE EXAMPLES 1 and 2

Fibers that had been manufactured as in Example 1 and cut to 51 mm werepacked into an Obermeyer dyeing machine at a packing density of 0.30g/cm³, and a hydrothermal treatment was performed for 90 minutes at 80°C. (Comparative Example 1), or a hydrothermal treatment was performedfor 10 minutes at 98° C. (Comparative Example 2), thus producing thedesired fibers.

COMPARATIVE EXAMPLE 3

Fibers were manufactured by the same method as in Example 1 using aspinning stock solution in which no PVAc was added to the spinning stocksolution used in Example 1. Next, appropriate oiling agent applicationand mechanical crimping were performed on these fibers using universallyknown methods, and the fibers were further cut to 51 mm. Afterward, thefibers were packed into an Obermeyer dyeing machine at a packing densityof 0.30 g/cm³, and were subjected to a hydrothermal treatment for 60minutes at 98° C. thus producing the desired fibers. A pore distributionmeasurement was performed for the fibers thus obtained; however, nopeaks indicating the presence of voids with diameters in the range of 1nm to 100 nm were detected.

COMPARATIVE EXAMPLE 4

An acrylic type copolymer consisting of 93 wt % acrylonitrile and 7 wt %vinyl acetate was dissolved in DMAc, and a spinning stock solution witha polymer concentration of 25 wt % was obtained by further adding 3parts by weight of PVAc to 100 parts by weight of the abovementionedacrylic type copolymer. This spinning stock solution was wet-spun via aspinning nozzle with 3900 holes having a hole size of 0.08×0.6 mm into asolidifying bath consisting of an aqueous solution with a 60%concentration of DMAc, and was further drawn to a draw ratio of 5.0times while the solvent was washed away in boiling water. Next, anoiling agent was applied, and the fibers were dried by means of hotrollers at 150° C. Afterward, the fibers were subjected to a relaxationtreatment in pressurized steam at a gauge pressure of 0.25 MPa, thusproducing fibers with a denier of 16.5 dtex. Next, appropriate oilingagent application and mechanical crimping were performed on these fibersusing universally known methods, and the fibers were further cut to 51mm. Afterward, the fibers were packed into a stainless steel basket, andthis basket was set in a pressurized steamer, where a saturated steamtreatment was performed for 1 minute at 110° C., thus producing thedesired fibers.

EXAMPLE 6

Fibers that had been manufactured as in Example 1 and cut 1 to 51 mmwere packed into an Obermeyer dyeing machine at a packing density of0.30 g/cm³, and a dyeing treatment was performed, thus producing thedesired fibers. The dyeing formula in this case was a dyeing formulaprepared by mixing the dyes Maxilon Yellow 2RL 200% 0.132% omf, MaxilonRed GRL 150% 0.054% omf, and Maxilon Blue GRL 300% 0.018% omf (allmanufactured by Ciba Specialty Chemical Inc.), and the dyeing assistantsLevenol WX (manufactured by Kao Co.) 0.5% omf and Ultra MT #100(manufactured by Mitejima Kagaku Co.) 0.5 g/L. Dyeing was performed withthe temperature elevated from room temperature at the rate of 3° C./min,and maintained for 60 minutes at a constant temperature when atemperature of 98° C. was reached.

EXAMPLE 7

Fibers that had been manufactured as in Example 1 and cut to 51 mm werepacked into an Obermeyer dyeing machine at a packing density of 0.30g/cm³, and a dyeing treatment was performed, thus producing the desiredfibers. The dyeing formula in this case was a dyeing formula prepared bymixing the dyes The dyeing formula in this case was a dyeing formulaprepared by mixing the dyes Maxilon Yellow 2RL 200% 0.0228% omf, MaxilonRed GRL 150% 0.0075% omf, and Maxilon Blue GRL 300% 0.0063% omf (allmanufactured by Ciba Specialty Chemical Inc.), and the dyeing assistantsLevenol WX (manufactured by Kao Co.) 0.5% omf and Ultra MT #100(manufactured by Mitejima Kagaku Co.) 0.5 g/L. Dyeing was performed withthe temperature elevated from room temperature at the rate of 3° C./min,and maintained for 60 minutes at a constant temperature when atemperature of 98° C. was reached.

Characteristic values and external appearance evaluation results for thefibers obtained in the abovementioned Examples 1 through 7 andComparative Examples 1 through 4 are shown in Table 1.

Furthermore, the measurement of the L value for the fibers obtained inExamples 1 through 5 and Comparative Examples 1 through 4 wasaccomplished as follows: specifically, the fibers obtained were dyedwith the temperature elevated from room temperature at the rate of 3°C./min and maintained at a constant temperature for 60 minutes when atemperature of 98° C. was reached, using a dying formula prepared bymixing the dyes Maxilon Yellow 2RL 200% 0.127 omf, Maxilon Red GRL 0.113omf, and. Maxilon Blue GRL 300% 0.118 omf (all manufactured by CibaSpecialty Chemical Inc.), and the dyeing assistants Levenol WX(manufactured by Kao Co.) 0.5% omf and Ultra MT #100 (manufactured byMitejima Kagaku Co.) 0.5 g/L. After dyeing was completed, the dyeingsolution was removed, and the dyed fabric material was dehydrated bycentrifuging and dried at 80° C. The L value was measured for the dyedfabric material thus obtained using the method described in (F) above.

TABLE 1 Acrylic type Amount of polyvinyl Treatment copolymer acetateadded Porosification time composition Solvent (parts by weight)treatment method (minutes) Example 1 AN/VCL Acetone 5 98° C. hot water60 Example 2 AN/VCL Acetone 5 105° C. pressurized steam 20 Example 3AN/VD Acetone 10  98° C. hot water 60 Example 4 AN/VAc DMAc 1 98° C. hotwater 60 Example 5 AN/VAc DMAc 1 105° C. pressurized steam 30 Example 6AN/VCL Acetone 5 98° C. dyeing 60 Example 7 AN/VCL Acetone 5 98° C.dyeing 60 Comparative AN/VCL Acetone 5 80° C. hot water 90 Example 1Comparative AN/VCL Acetone 5 98° C. hot water 10 Example 2 ComparativeAN/VCL Acetone 0 98° C. hot water 60 Example 3 Comparative AN/VAc DMAc 3110° C. pressurized steam  1 Example 4 Fiber cross- Rate of sectionaldrop in Rate of drop length True specific Specific specific in specificExternal Major- Minor- gravity of gravity of gravity gravity causedappearance axis axis acrylic type porosified from true by of porouslength length Flattening copolymer fibers specific porosification Lacrylic (μm) (μm) ratio (g/cm³) (g/cm³) gravity (%) (%) value fibersExample 1 115 18 6.4 1.28 1.15 10.0 8.0 53.0 ⊚ Example 2 115 18 6.4 1.281.16 9.4 7.2 53.0 ⊚ Example 3 118 19 6.2 1.35 1.12 17.0 8.2 49.8 ⊚Example 4 120 17 7.1 1.17 1.08 7.7 7.8 48.8 ⊚ Example 5 120 18 6.7 1.171.07 8.5 8.5 48.8 ⊚ Example 6 115 18 6.4 1.28 1.15 10.0 8.0 53.0 ⊚Example 7 115 18 6.4 1.28 1.15 10.0 8.0 53.0 ⊚ Comparative 113 18 6.31.28 1.27 0.8 0.1 33.8 X Example 1 Comparative 113 19 5.9 1.28 1.25 2.32.3 40.1 X Example 2 Comparative 123 18 6.8 1.28 1.28 0 0 32.4 X Example3 Comparative 117 17 6.9 1.17 1.14 2.6 1.7 36.8 X Example 4 Note) In thepolymer compositions shown in the table, AN indicates acrylonitrile, VCLindicates vinyl chloride, VD indicates vinylidene chloride, and VAcindicates vinyl acetate.

Furthermore, the pore distribution of the dyed fabric material obtainedin Example 1 was measured. The pore volume, porosity and the likeobtained as a result of this measurement are shown in Table 2.

TABLE 2 Pore volume Mean diameter Porosity Sample volume (weight) Vp; CC· CC⁻¹ D; nm P; % V; cc (W; g) 0.061 24 6.4 0.179 (0.1872)

In Table 2, Vp indicates the cumulative volume of mercury injected atthe measurement pressure, and P indicates the porosity;here, P=(Vp×W)/V[W:sample weight, V:sample volume].

Measurements were performed by the mercury pressure injection methodusing a Porosimeter—Pore Sizer 9320 manufactured by Micrometrics Co.Approximately 0.2 g of each sample was weighed out using an electronicbalance (AEL200) manufactured by Shimazu Seisakusho;this sample wasplaced in the measurement cell, and mercury was injected under reducedpressure. The cell was then mounted in the apparatus and subjected tomeasurement. The measurement conditions are shown below.

Measurement pressure range: approximately 3.7 kPa to 207 MPa (porediameter; approximately 70 angstroms to 400 μm)

Measurement mode; pressure elevation process in the abovementionedpressure range (1st run)

Cell volume: 5 cm³

Number of measurements: 2

EXAMPLE 8

An acrylic type copolymer consisting of 49 wt % acrylonitrile, 50 wt %vinyl chloride and 1 wt % sodium styrenesulfonate was dissolved inacetone at the rate of 30 wt %. An acetone solution in which PVAc wasdissolved at a concentration of 40 wt % was added to the abovementionedacetone solution so that the PVAc content of the resulting solution was5 parts by weight per 100 parts by weight of the abovementioned acrylictype copolymer; furthermore, an acetone solution in which celluloseacetate with a degree of acetification of 55% was dissolved at the rateof 15 wt % was added to the abovementioned solution so that thecellulose acetate content of the resulting solution was 2.0 parts byweight per 100 parts by weight of the abovementioned acrylic typecopolymer, and the solution obtained by mixing and agitating theseingredients was used as a spinning stock solution. This spinning stocksolution was discharged into a solidifying bath consisting of a 25 wt %aqueous solution of acetone at 35° C. via a spinning nozzle with 400rectangular slit-form holes having dimensions of 0.08 mm×0.6 mm, and thespun fibers were taken up by a roller at a take-up rate of 2 m/min.Next, drawing to a draw ratio of 1.4 times was applied in a 55 wt %aqueous solution of acetone at 25° C., and drawing to a draw ratio of1.36 times was further applied in a 25 wt % aqueous solution of acetoneat 25° C. Afterward, the fibers were rinsed with water via a water rinsebath at 40° C. and a water rinse bath at 75° C., and the fibers werethen rinsed again while being drawn to a draw ratio of 1.5 times in awater rinse bath at 75° C. The fibers were then oiled. Next, after beingdried in a uniform-heat air draft drier at 130° C., the fibers werefurther drawn to a draw ratio of 2 at the same temperature, and werethen subjected to a heat treatment at 145° C. The fibers thus obtainedhad a denier of 17.5 dtex and fiber specific gravity of 1.28;furthermore, according to SEM observation, the major-axis width of thefiber cross section was 111 μm. Appropriate oiling agent application andpi mechanical crimping were performed on these fibers using universallyknown methods, and the fibers were further cut to 51 mm; afterward, thefibers were dyed with the temperature elevated from room temperature atthe rate of 3° C./min and maintained at a constant temperature for 60minutes when a temperature of 98° C. was reached, using a dying formulaprepared by mixing the dyes Maxilon Yellow 2RL 200% 0.127 omf. MaxilonRed GRL 0.113 omf, and Maxilon Blue GRL 300% 0.118 omf (all manufacturedby Ciba Specialty Chemical Inc.), and the dyeing assistants Levenol WX(manufactured by Kao Co.) 0.5% omf and Ultra MT #100 (manufactured byMitejima Kagaku Co.) 0.5 g/L. After dyeing was completed, the dyeingsolution was removed, and the dyed fabric material was dehydrated bycentrifuging and dried at 80° C. In regard to the external appearance ofthe fibers following dyeing, the fibers appeared thicker than those ofthe fabric material prepared in Comparative Examples 5 through 7described below. Furthermore, the dyed fabric material consisting ofthese fibers was a dyed fabric material with a superior externalappearance, in which the L value was 49.8 and the rate of the drop inspecific gravity caused by dyeing was 6.2%; moreover, SEM observationshowed this fabric material to have a more or less rectangular crosssection in which the major-axis width of the fiber cross section was 113μm and the minor-axis width was 18 μm (flattening ratio: 6.3), and thefeeling of the presence of individual fibers was conspicuous.

COMPARATIVE EXAMPLE 5

Fibers were manufactured in exactly the same manner as in Example 8,except that the respective acetone solutions of PVAc and celluloseacetate that were added to the spinning stock solution in Example 8 werenot added. The fibers thus obtained had a denier of 18.2 dtex and afiber specific gravity of 1.29; furthermore, it was found from SEMobservation that the major-axis width of the fiber cross section was 115μm. Appropriate oiling agent application and mechanical crimping wereperformed on these fibers using universally known methods, and thefibers were further cut to 51 mm; afterward, the fibers were dyed in thesame manner as in Example 8. When the characteristics of the dyed fabricmaterial were measured, it was found that the L value was 38.3 and thedrop in specific gravity caused by dyeing was 0.5%. SEM observationindicated that the fibers had a more or less rectangular cross sectionin which the major-axis width of the fiber cross section was 116 μm andthe minor-axis width was 18 μm (flattening ratio: 6.4): however, almostno porosification was observed.

COMPARATIVE EXAMPLE 6

Fibers were manufactured in exactly the same manner as in ComparativeExample 5, except that the shape of the slits in the spinning nozzleused in Comparative Example 5 was changed to a round shape with a holediameter of 0.22 mm. As a result, fibers with a denier of 17.2 dtex wereobtained. Appropriate oiling agent application and mechanical crimpingwere performed on these fibers using universally known methods, and thefibers were further cut to 51 mm; afterward, the fibers were dyed in thesame manner as in Example 8. When the characteristics of the dyed fabricmaterial were measured, it was found that the L value was 33.7 and thedrop in specific gravity caused by dyeing was 0%; no porosification wasobserved. Furthermore, SEM observation indicated that the fibers had anopen C-form cross-sectional shape in which the major-axis width of thefiber cross section was 69 μm and the minor-axis width was 29 μm(flattening ratio: 2.4). The external appearance of the fibers showedlittle feeling of the presence of the individual fibers.

COMPARATIVE EXAMPLE 7

A uniformly mixed and dissolved acetone solution containing 29.5 wt %acrylic type copolymer consisting of 49 wt % acrylonitrile, 50 wt %vinyl chloride and 1 wt % sodium styrenesulfonate, and 0.59 wt %cellulose acetate with a degree of acetification of 56%, was used as aspinning stock solution. This spinning stock solution was dischargedinto a solidifying bath consisting of a 25 wt % aqueous solution ofacetone at 35° C. via a spinning nozzle with 400 rectangular slit-formholes having dimensions of 0.08 mm×0.6 mm. The spun fibers were taken upby a roller at a take-up rate of 2 m/min; next, drawing to a draw ratioof 1.4 times was applied in a 55 wt % aqueous solution of acetone at 25°C., and drawing to a draw ratio of 1.36 times was further applied in a25 wt % aqueous solution of acetone at 25° C. Afterward, the fibers wererinsed with water via a water rinse bath at 40° C. and a water rinsebath at 75° C., and the fibers were then rinsed again while being drawnto a draw ratio of 1.5 times in a water rinse bath at 75° C. The fiberswere then oiled. Next, after being dried in a uniform-heat air draftdrier at 130° C., the fibers were further drawn to a draw ratio of 2 atthe same temperature, and were then subjected to a heat treatment at145° C., thus producing fibers with a denier of 17.3 dtex. Appropriateoiling agent application and mechanical crimping were performed on thesefibers using universally known methods, and the fibers were further cutto 51 mm; afterward, the fibers were dyed in the same manner as inExample 8. As a result, the dyed fabric material consisting of thesefibers showed an L value of 39.4, and the rate of drop in the specificgravity caused by dyeing was 0%, so that no porosification was observed.Furthermore, SEM observation indicated that the fibers had a more orless rectangular cross-sectional shape in which the major-axis width ofthe fiber cross section was 107 μm and the minor-axis width was 21 μm(flattening ratio: 5.1). The external appearance of the fibers showedlittle feeling of the presence of the individual fibers.

EXAMPLE 9

An acetone solution containing 27 wt % acrylic type copolymer consistingof 52 wt % acrylonitrile, 47 wt % vinylidene chloride and 1 wt % sodiumstyrenesulfonate, 2.7 wt % PVAc and 0.27 wt % cellulose acetate with adegree of acetification of 54% was uniformly mixed and dissolved to forma spinning stock solution. This spinning stock solution was dischargedinto a solidifying bath consisting of a 25 wt % aqueous solution ofacetone at 35° C. via a spinning nozzle with 150 rectangular slit-formholes having dimensions of 0.05 mm×0.43 mm. The spun fibers were takenup by a roller at a take-up rate of 2.5 m/min; next, drawing to a drawratio of 1.4 times was applied in a 55 wt % aqueous solution of acetoneat 25° C., and drawing to a draw ratio of 1.36 times was further appliedin a 25 wt % aqueous solution of acetone at 25° C. Afterward, the fiberswere rinsed with water via a water rinse bath at 40° C. and a waterrinse bath at 75° C., and the fibers were then rinsed again while beingdrawn to a draw ratio of 1.58 times in a water rinse bath at 75° C. Thefibers were then oiled. Next, after being dried in a uniform-heat airdraft drier at 130° C., the fibers were further drawn to a draw ratio of2.25 at the same temperature, and were then subjected to a heattreatment at 145° C., thus producing fibers with a denier of 11.6 dtexin which the major-axis width of the fiber cross section (as seen fromSEM observation) was 83 μm. Appropriate oiling agent application andmechanical crimping were performed on these fibers using universallyknown methods, and the fibers were further cut to 51 mm; afterward, thefibers were dyed in the same manner as in Example 8. As a result, thedyed fabric material consisting of these fibers was a dyed fabricmaterial with a superior external appearance, in which the L value was48.7 and the rate of the drop in specific gravity caused by dyeing was4.3%; moreover, SEM observation showed this fabric material to have amore or less rectangular cross section in which the major-axis width ofthe fiber cross section was 85 μm and the minor-axis width was 22 μm(flattening ratio: 3.9), and the feeling of the presence of individualfibers was conspicuous.

COMPARATIVE EXAMPLE 8

Fibers were manufactured in exactly the same manner as in Example 9except that the PVAc and cellulose acetate added to the spinning stocksolution in Example 9 were not added. As a result, fibers with a denierof 11.8 dtex were obtained. When these fibers were dyed in the samemanner as in Example 8, the dyed fabric material consisting of thesefibers showed an L value of 35.7, and the rate of drop in the specificgravity caused by dyeing was 0.8%, so that almost no porosification wasobserved. Furthermore, SEM observation indicated that the fibers had amore or less rectangular cross-sectional shape in which the major-axiswidth of the fiber cross section was 120 μm and the minor-axis width was15 μm (flattening ratio: 8.0). The external appearance of the fibersshowed little feeling of the presence of the individual fibers.

EXAMPLE 10

An acrylic type copolymer consisting of 49 wt, % acrylonitrile, 50 wt %vinyl chloride and 1 wt % sodium styrenesulfonate was dissolved inacetone at the rate of 30 wt %. An acetone solution in which PVAc wasdissolved at a concentration of 40 wt % was added to the abovementionedacetone solution so that the PVAc content of the resulting solution was1 part by weight per 100 parts by weight of the abovementioned acrylictype copolymer; furthermore, an acetone solution in which celluloseacetate with a degree of acetification of 55% was dissolved at the rateof 15 wt % was added to the abovementioned solution so that thecellulose acetate content of the resulting solution was 10 parts byweight per 100 parts by weight of the abovementioned acrylic typecopolymer, and the solution obtained by mixing and agitating theseingredients was used as a spinning stock solution. This spinning stocksolution was discharged into a solidifying bath consisting of a 25 wt %aqueous solution of acetone at 35° C. via a spinning nozzle with 50rectangular slit-form holes having dimensions of 0.1 mm×0.85 mm, and thespun fibers were taken up by a roller at a take-up rate of 4 m/min.Next, drawing to a draw ratio of 1.5 times was applied in a 55 wt %aqueous solution of acetone at 25° C., and drawing to a draw ratio of1.02 times was further applied in a 25 wt % aqueous solution of acetoneat 25° C. Afterward, the fibers were rinsed with water via a water rinsebath at 40° C. and a water rinse bath at 75° C., and the fibers werethen rinsed again while being drawn to a draw ratio of 1.25 times in awater rinse bath at 75° C. The fibers were then oiled. Next, after beingdried in a uniform-heat air draft drier at 130° C., the fibers werefurther drawn to a draw ratio of 1.5 at the same temperature, and werethen subjected to a heat treatment at 145° C. The fibers thus obtainedhad a denier of 44.8 dtex; furthermore, according to SEM observation,the major-axis width of the fiber cross section was 185 μm, and thefibers had a superior external appearance with an extremely strongfeeling of the presence of the individual fibers. Appropriate oilingagent application and mechanical crimping were performed on these fibersusing universally known methods, and the fibers were further cut to 51mm; afterward, the fibers were dyed in the same manner as in Example 8.As a result, the dyed fabric material consisting of these fibers was adyed fabric material with a superior external appearance, in which the Lvalue was 43.8 and the rate of the drop in specific gravity caused bydyeing was 8.0%; moreover, SEM observation showed this fabric materialto have a more or less rectangular cross section in which the major-axiswidth of the fiber cross section was 190 μm and the minor-axis width was35 μm (flattening ratio: 5.4), and the feeling of the presence ofindividual fibers was conspicuous.

Characteristic values and external appearance evaluation results for thefibers obtained in the abovementioned Examples 8 through 10 andComparative Examples 5 through 8 are shown in Table 3.

TABLE 3 Acrylic type Amount of polyvinyl copolymer acetate addedCellulose acetate Porosification Treatment time composition Solvent(parts by weight) (parts by weight) treatment method (minutes) Example 8AN/VCL Acetone 5 2 98° C. dyeing 60 Example 9 AN/VD Acetone 10  1 98° C.dyeing 60  Example 10 AN/VCL Acetone 1 10  98° C. dyeing 60 ComparativeAN/VCL Acetone 0 0 98° C. dyeing 60 Example 5 Comparative AN/VCL Acetone0 0 98° C. dyeing 60 Example 6 Comparative AN/VCL Acetone 0 2 98° C.dyeing 60 Example 7 Comparative AN/VD DMAc 0 0 98° C. dyeing 60 Example8 Fiber cross- Rate of sectional drop in Rate of drop length Truespecific Specific specific in specific External Major- Minor- gravity ofgravity of gravity gravity caused appearance axis axis acrylic typeporosified from true by of porous length length Flattening copolymerfibers specific porosification L acrylic (μm) (μm) ratio (g/cm³) (g/cm³)gravity (%) (%) value fibers Example 8 113 18 6.3 1.28 1.20 6.3 6.2 49.8◯ Example 9  85 22 3.9 1.34 1.24 7.5 4.3 48.7 ◯  Example 10 190 35 5.41.28 1.18 7.8 8.0 43.8 ⊚ Comparative 116 18 6.4 1.28 1.28 0 0.5 38.3 XExample 5 Comparative  69 29 2.4 1.28 1.28 0 0 33.7 X Example 6Comparative 107 21 5.1 1.28 1.27 0.8 0 39.4 X Example 7 Comparative 12015 8.0 1.35 1.35 0 0.8 35.7 X Example 8 Note) In the polymercompositions shown in the table, AN indicates acrylonitrile, VCLindicates vinyl chloride, VD indicates vinylidene chloride, and VAcindicates vinyl acetate.

EXAMPLES 11˜15

Five types of pile fabrics (Examples 11 through 15) were prepared bymixing 70 parts by weight of each of the fabrics obtained in Examples 1through 5 with 30 parts by weight of the commercially marketed acrylicfibers “Kanekalon (registered trademark) SL” (3.3 dtex, 32 mm;manufactured by Kanegafuchi Kagaku Kogyo K.K.). The final weight of thepile fabrics in this case was 950 g/m², and the mean pile length was 20mm. As is shown in Table 4, the pile fabrics thus obtained showedsuperior external appearance characteristics in which the presence ofthe individual fibers of the pile part was emphasized to a considerableextent.

COMPARATIVE EXAMPLES 9˜12

Four types of pile fabrics (Comparative Examples 9 through 12) wereprepared by mixing 70 parts by weight of each of the fibers obtained inComparative Examples 1 through 4 with the commercially marketed acrylicfibers “Kanekalon (registered trademark) SL” (3.3 dtex, 32 mm;manufactured by Kanegafuchi Kagaku Kogyo K.K.). The final weight of thepile fabrics in this case was 950 g/m², and the mean pile length was 20mm. In the pile fabrics thus obtained, as is shown in Table 4, thefeeling of the presence of the individual fibers in the pile part wasfairly poor.

TABLE 4 Weight Mean of External Proportions of fibers pile pileappearance used Construction length fabric of pile (parts by weight) ofpile (mm) (g/cm²) fabric Example 11 Example 1/SL = 70/30 Plain 20 950 ◯construction with uniform pile length Example 12 Example 2/SL = 70/30Plain 20 950 ◯ construction with uniform pile length Example 13 Example3/SL = 70/30 Plain 20 950 ◯ construction with uniform pile lengthExample 14 Example 4/SL = 70/30 Plain 20 950 ◯ construction with uniformpile length Example 15 Example 5/SL = 70/30 Plain 20 950 ◯ constructionwith uniform pile length Comparative Comparative Example Plain 20 950 XExample 9 1/SL = 70/30 construction with uniform pile length ComparativeComparative Example Plain 20 950 X Example 10 2/SL = 70/30 constructionwith uniform pile length Comparative Comparative Example Plain 20 950 XExample 11 3/SL = 70/30 construction with uniform pile lengthComparative Comparative Example Plain 20 950 X Example 12 4/SL = 70/30construction with uniform pile length

EXAMPLES 16 and 17 COMPARATIVE EXAMPLE 13

Pile fabrics were prepared by mixing 30 parts by weight of the acrylicfiber obtained in Example 1, 50 parts by weight of the commerciallymarketed acrylic fiber “Kanekalon (registered trademark) RLM (BR517)”(12 dtex, 44 mm; manufactured by Kanegafuchi Kagaku Kogyo K.K.) and 20parts by weight of the commercially marketed acrylic fiber “Kanekalon(registered trademark) AHD (10)” (4.4 dtex, 32 mm; manufactured byKanegafuchi Kagaku Kogyo K.K.) (Example 16), mixing 10 parts by weightof the acrylic fiber obtained in Example 1, 70 parts by weight of theabovementioned acrylic fiber “Kanekalon (registered trademark) RLM(BR517)” and 20 parts by weight of the abovementioned acrylic fiber“Kanekalon (registered trademark) AHD (10)” (Example 17), and mixing 2parts by weight of the acrylic fiber obtained in Example 1, 78 parts byweight of the abovementioned acrylic fiber “Kanekalon (registeredtrademark) RLM (BR517)” and 20 parts by weight of the abovementionedacrylic fiber “Kanekalon (registered trademark) AHD (10)” (ComparativeExample 13). The final weight of the pile fabrics in this case was 950g/m², the mean pile length was 20 mm, and the step difference was 6 mm.As is shown in Table 5, the pile fabrics obtained in Examples 16 and 17showed superior external appearance characteristics in which a feelingof the presence of the individual fibers of the pile part was emphasizedto a considerable extent; however, in the case of Comparative Example13, the feeling of the presence of the individual fibers of the pilepart was fairly poor.

TABLE 5 Proportion of Mean pile Proportions of fibers of length ofWeight External construction of overall Example 1 in long pile Step ofpile appearance Proportions of fibers used pile part, long long pilepart part difference* fabric of pile (parts by weight) pile/short pile(wt %) (wt %) (mm) (mm) (g/cm²) fabric Example 16 Example 1/RLM/AHD =30/50/20 80/20 37.5 20 6 950 ◯ Example 17 Example 1/RLM/AHD = 10/70/2080/20 12.5 20 6 950 ◯ Comparative Example 1/RLM/AHD = 2/78/20 80/20 2.520 6 950 X Example 13 *Step difference: difference in mean pile lengthbetween long pile and short pile

EXAMPLES 18˜20 COMPARATIVE EXAMPLE 14

Pile fabrics were prepared by mixing 10 parts by weight of the acrylicfabric obtained in Example 6 and 90 parts by weight of the commerciallymarketed acrylic fiber “Kanekalon (registered trademark) AHD (10)” (4.4dtex, 32 mm; manufactured by Kanegafuchi Kagaku Kogyo K.K.) (Example18), and by mixing 2 parts by weight of the acrylic fiber obtained inExample 6 and 98 parts by weight of the abovementioned acrylic fiber“Kanekalon (registered trademark) AHD (10)” (Comparative Example 14).The final weight of the pile fabrics in this case was 880 g/m², the meanpile length was 15 mm, and the step difference was 4 mm. Similarly, pilefabrics were prepared by mixing 30 parts by weight of the acrylic fiberobtained in Example 7 and 70 parts by weight of the commerciallymarketed acrylic fiber “Kanekalon (registered trademark) AH (740)” (5.6dtex, 38 mm; manufactured by Kanegafuchi Kagaku Kogyo K.K.) (Example19), and by mixing 10 parts by weight of the acrylic fiber obtained inExample 7, 20 parts by weight of the commercially marketed acrylic fiber“Kanekalon (registered trademark) RCL” (17 dtex, 51 mm; manufactured byKanegafuchi Kagaku Kogyo K.K.), and 70 parts by weight of theabovementioned acrylic fiber “Kanekalon (registered trademark) AH (740)”(Example 20). The final weight of the pile fabrics in this case was 900g/m² in all of the fabrics, the mean pile length was 47 mm, and the stepdifference was 25 mm. As is shown in Table 6, the pile fabrics obtainedin Examples 18 through 20 showed superior external appearancecharacteristics in which a feeling of the presence of the individualfibers of the pile part was emphasized to a considerable extent;however, in the case of Comparative Example 14, the feeling of thepresence of the individual fibers of the pile part was fairly poor.

TABLE 6 Proportion of Mean pile Proportions of fibers of length ofWeight External construction of overall Example 1 in long pile Step ofpile appearance Proportions of fibers used pile part, long long pilepart part difference* fabric of pile (parts by weight) pile/short pile(wt %) (wt %) (mm) (mm) (g/cm²) fabric Example 18 Example 6/AHD = 10/9010/90 100 15  4 880 ◯ Comparative Example 6/AHD = 2/98  2/98 100 15  4880 Δ Example 14 Example 19 Example 7/AH = 30/70 30/70 100 47 25 900 ◯Example 20 Example 7/RCL/AH = 10/20/70 30/70 33.3 47 25 900 ◯ *Stepdifference: difference in mean pile length between long pile and shortpile

Industrial Applicability

The porous acrylic fiber is porosified in an after-process followingspinning, crimping and cutting, so that a feeling of the presence of theindividual fibers is emphasized. Furthermore, a porous structure caneasily be obtained by performing a hydrothermal treatment or saturatedsteam treatment such as a dyeing operation or the like followingspinning, crimping and cutting. Accordingly, for fiber makers, thepresent invention has the merit of not requiring the addition of specialconditions or apparatus to the manufacturing process accompanyingporosification. Furthermore, the pile fabric of the present inventionconsisting of the abovementioned porous acrylic fiber has extremelysuperior external appearance characteristics in which a feeling of thepresence of the individual fibers forming the pile part appears to beemphasized. As a result, a novel product design which is superior indesign characteristics for clothing, toys (stuffed animals) and interioruse or the like can be obtained.

What is claimed is:
 1. A porous acrylic fiber that is mainly composed ofa resin composition containing 0.3 to 20 parts by weight of polyvinylacetate based on 100 parts by weight of an acrylic type copolymer, saidfiber being characterized in that a denier of the fiber is 2 to 50 dtex,a flattening ratio of the fiber cross section (ratio of a major-axiswidth to a minor-axis width) is 2.5 to 25, the major-axis width is 70 to300 μm, and the rate of the drop in specific gravity thereof is in therange of 5.0 to 20% when calculated by the Equation Rate of drop inspecific gravity (%)=100×(1−Da/Db) where, Da indicates the specificgravity value of the porous acrylic fiber, and Db indicates the truespecific gravity value of the resin consisting of the acrylic typecopolymer.
 2. The porous acrylic fiber according to claim 1, whereinsaid acrylic type copolymer is a copolymer consisting essentially of 35to 98 wt % acrylonitrile and 2 to 65 wt % other vinyl type monomer(s)copolymerizable with acrylonitrile.
 3. The porous acrylic fiberaccording to claim 1, wherein said acrylic type copolymer is a copolymerconsisting essentially of 35 to 98 wt % acrylonitrile, 2 to 65 wt %vinyl chloride and/or vinylidene chloride, and 0 to 10 wt %sulfonate-group-containing vinyl type monomer(s) copolymerizable withthese compounds.
 4. The porous acrylic fiber according to claim 1,wherein said resin composition contains 0.3 to 20 parts by weight ofpolyvinyl acetate and 0.5 to 15parts by weight of cellulose resin basedon 100 parts by weight of acrylic type copolymer.
 5. The porous acrylicfiber according to claim 4, wherein said cellulose resin consists of atleast one resin selected from a group consisting of cellulose acetate,cellulose propionate and cellulose acetate butyrate.
 6. A method forproducing the porous acrylic fiber according to claim 1, characterizedin that fibers formed by wet-spinning a spinning stock solutioncontaining 0.3 to 20 parts by weight of polyvinyl acetate based on 100parts by weight of an acrylic type copolymer so that a denier of thefiber is 2 to 50 dtex, a flattening ratio of the fiber cross section(ratio of a major-axis width to a minor-axis width) is 2.5 to 25, andthe major-axis width is 70 to 300 μm, are subjected to crimping andcutting treatments, and are then porosified by a hydrothermal treatmentfor 30 to 120 minutes at 90 to 100° C. and/or a saturated steamtreatment for 10 to 90 minutes at 90to 130° C.
 7. A method for producingthe porous acrylic fiber according to claim 4, characterized in thatfibers formed by wet-spinning a spinning stock solution containing 0.3to 20 parts by weight of polyvinyl acetate and 0.5 to 15 parts by weightof a cellulose resin based on 100 parts by weight of an acrylic typecopolymer so that a denier of the fiber is 2 to 50 dtex, a flatteningratio of the fiber cross section (ratio of a major-axis width to aminor-axis width) is 2.5 to 25, and the major-axis width is 70 to 300μm, are subjected to crimping and cutting treatments, and are thenporosified by a hydrothermal treatment for 30 to 120 minutes at 90 to100° C. and/or a saturated steam treatment for 10 to 90 minutes at 90 to130° C.
 8. The method for producing a porous acrylic fiber according toclaim 6 or claim 7, wherein the hydrothermal treatment is a dyeingoperation.
 9. The porous acrylic fiber produced by the method accordingto claims 6 or 7, wherein the rate of the drop in specific gravity is inthe range of 3.0 to 15% when calculated from the specific gravity (Dp)before porosification and the specific gravity (Da) of the porosifiedfiber by the Equation Rate of drop in specific gravity(%)=100×(1−Da/Dp).
 10. A pile fabric comprising the porous acrylic fiberaccording to any one of claims 1 through 5, 6 and
 7. 11. The pile fabricaccording to claim 10, which contains said porous acrylic fiber at therate of 3 wt % or greater in the pile part.
 12. The pile fabricaccording to claim 10, which is a pile fabric having a step differencethat has at least a long pile part and a short pile part, wherein saidporous acrylic fiber is contained in the long pile part.
 13. The pilefabric according to claim 12, wherein said porous acrylic fiber iscontained in the fibers of the overall pile part at the rate of 5 to 60wt %.
 14. The pile fabric according to claim 12, wherein the differencebetween the mean pole length of the long pile part and the mean pilelength of the short pile part in said pile fabric having a stepdifference is 2 mm or greater, and the mean pile length of the long pilepart is 12 to 70 mm.